Electrical stimulation of bodily parts such as spinal cord, peripheral nerves, cranial nerves, nerve roots, muscles, or brain tissues is used to treat various conditions including, for example, Parkinson's disease, dystonia, chronic pain, Huntington's disease, bradykinesia, epilepsy and seizures, eating disorders, and mood disorders. For those conditions as well as others, sensing or recording electrodes are also available for monitoring the electrical activity of the tissues to be treated or studied. Many of the electrodes, whether stimulating or sensing electrodes, have similar characteristics.
Typically, an electrode for stimulation comprises a flexible, axially extending probe body with several annular or other structural stimulation contacts distributed at equal or different distances along a region of the probe body. Similar electrodes can be built for recording physiological potentials and neural activity in those tissues, especially brain tissues.
While optimizing stimulation of the electrodes based on therapeutic results, a finer shaping of the electrical field formed by the electrode is required, which in turn will shape an activating field (the activation field is the actual area in the brain being affected by neuronal elements being activated and or inhibited by produced electrical field). By directing the activation field towards desired tissue region and limiting its extent from other regions, much better optimization can be performed, while increasing the therapeutic benefit to the patient and decreasing the side effects from the stimulation as partially done with today's technologies only along the electrode lead and not in directions perpendicular to the lead axis. Optimizing the shape of the activation field requires, among other, to increase the number and resolution of the electrode contacts so as to increase the resolution of the activation field that can be accomplished. Therefore, the directionality of the electrode contacts is very important.
Currently marketed electrodes contain limited number of contacts; these electrodes are assembled manually or in a semi-automatic manner. Future approaches are directed towards other methods of electrode lead manufacturing like Lithographic etching, electroforming, laser ablation and other to precisely manufacture electrode arrays with finer contacts and higher number of contacts. However, these methods are cumbersome and the procedure is relatively long and as a rule, have limited and essentially two-dimensional surfaces, As the contact surface is smaller, the area contacting the body fluid or body tissue becomes smaller as well and the electrical properties of the electrode are worsens (e.g. impedance of contact increases), resulting in potentially high current densities that might be harmful. It is extremely difficult to produce arrays of small electrodes having complex shapes with a large number of conductive surfaces, in particular asymmetric arrays that can be crucial in treating conditions as mentioned.
U.S. Pat. No. 5,330,524 discloses an implantable cardiac defibrillation electrode, in which there is an electrically conductive wire mesh formed of crossed spirally wound cables. Each of the spirally wound cables includes a plurality of stranded wire elements, with a central wire element and a plurality of outer wire elements wound adjacent to the central wire element. Such electrodes do provide flexibility and a large contact surface area; however, the meshes described in U.S. Pat. No. 5,330,524 are electrically conductive in their entirety, but are not sufficiently directional or area-specific for some applications.
Another example is described by Parker at al. in U.S. Pat. No. 8,923,984. The disclosure depicts neurostimulator made of a knitted electrode. In this case, there is a possibility to form contact areas that are more specific since a conductive filament is intertwined within non-conductive filaments. Among other disadvantages of the disclosed structure, the knitted electrode has relative large spacing between adjacent rows, a fact that prevents accurate and stable positioning of the electrode in a desired area that is usually very small.
The present invention, on the other hand, aims at addressing the need for more specificity in controlling the size and positioning of the very small contacts on the electrode lead according to an aspect of the invention as well as their critical properties their directionality and their electrical properties (e.g. impedance). The electrode lead according to the present invention is easily and accurately fabricated.